We will extend a line of investigation that suggests that "multiple hits", consisting of mishandling of 1) alphasynuclein (a-syn) degradation, 2) cytosolic calcium, and 3) cytosolic dopamine (DA), underlie Parkinson's disease (PD). Our preliminary results indicate that if any of these factors are absent in neuronal culture models of selective substantia nigra (SN) death, neurodegeneration can be blocked. During the prior Udall period, we 1) developed intracellular patch electrochemistry (IPE) to measure cytosolic dopamine (Mosharov et al., 2003;Mosharov et al., 2006b) and 2) reported that a-syn is specifically degraded within specialized lysosomes by chaperone-mediated autophagy (CMA), but that pathogenic a-syn mutants and DA-modified-a-syn (DA-syn) block CMA (Cuervo et al., 2004;Martinez-Vicente et al., 2008). In the current proposal, we characterize how a-syn is trafficked to lysosomes and blocks CMA (Aim 1) how cytosolic Ca++ controls cytosolic DA in SN neurons (Aim 2) and how the combination of these three "hits" disturbs normal homeostasis and may cause in pathology in mice (Aim 3).